Evanescent fiber-optic chemical sensor for monitoring volatile organic compounds in water

The transport of trichloroethylene, 1,1,1-trichloroethane, and toluene in aqueous solutions through a polydimethylsiloxane film was modeled using a Fickian diffusion model to fit data obtained from an evanescent fiber-optic chemical sensor (EFOCS). The resultant diffusion coefficients for these analytes were respectively 3 × 10(-)(7), 5 × 10(-)(7), and 1 × 10(-)(7) cm(2)/s. Inclusion of an interfacial conductance term, defined as the ratio of the mass transport coefficient across the polymer surface and the analyte diffusion coefficient in the polymer, was required to accurately model the data. It was determined that the interfacial conductance terms were generally of the same order of magnitude for the analytes examined, suggesting a constant transport mechanism for the analytes. Linear chemometric algorithms were used to model the EFOCS response to aqueous mixtures of the three analytes with individual analyte concentrations between 20 and 300 ppm. Both partial least-squares and principal component regression algorithms performed comparably on the calibration sets, with cross-validated root-mean-squared errors of prediction for trichloroethylene, 1,1,1-trichloroethane, and toluene of approximately 26, 29, and 22 ppm, respectively. The resultant prediction model was then used to determine analyte concentrations in an independent data set with comparable precision.     

Detection of volatile compounds with mass-sensitive sensor arrays in the presence of variable ambient humidity

Mass-sensitive sensor arrays were established for the detection of isomeric or highly analogue analyte mixtures, which show similar physical and morphological properties. Supramolecular host-guest chemistry and arrays of four mass-sensitive quartz crystal microbalances have been successfully combined with multivariate calibration techniques in the presence of variable air moisture. This system enabled even the separation of xylene isomers [Formula: see text] a task that might be crucial even by gas chromatography. The data of the sensor arrays were analyzed with partial least squares and artificial neural networks. The xylene isomers could be detected with an accuracy of ～1% in the range of 0-200 ppm, nearly eliminating the residual water cross-sensitivity of the sensor coatings, which allows effective work place or environmental monitoring of toxic compounds with fast response levels.     

Optical D-fiber-based volatile organic compound sensor

A fiber-optic sensor used to detect volatile organic compounds is described. The sensor consists of a single-mode D-fiber with a 2.5 microm polydimethylsiloxane layer. The layer is applied to the fiber flat after removal of a section of the fiber's cladding to increase evanescent interaction of the light with the layer. Absorption of volatile organic compounds into the polymer alters the refractive index of the layer, resulting in a birefringent change of the fiber. This change is observed as a shift in polarization of the light carried by the fiber. The sensor has a short length of 3 cm and a response time of around 1 s. The sensor is naturally reversible and gives an exponential response for gas and liquid concentrations of dichloromethane and acetone, respectively.     

Bioconcentration factors for volatile organic compounds in vegetation

Samples of air and leaves were taken at the University of Nevada [Formula: see text] Las Vegas campus and analyzed for volatile organic compounds using vacuum distillation coupled with gas chromatography/mass spectrometry. The data were used to estimate the bioconcentration of volatile organic compounds (VOCs) and to characterize the equilibration of VOCs between the leaves and air. The bioconcentration of volatiles in the leaves of some species can be predicted using the partition coefficients between air and octanol (K(oa)) and only considering VOC absorption in the lipid fraction of leaves. For these leaves, the bioconcentration factors agreed with existing models. Leaves of some species displayed a bioconcentration of volatiles that greatly exceeded theory. These hyperbioconcentration leaves also contain appreciable concentrations of monoterpenes, suggesting that a terpenoid compartment should be considered for the bioconcentration of organic compounds in leaves. Adding an additional "terpenoid" compartment should improve the characterization of volatile organic compounds in the environment. The uptake of VOCs from air by leaves is rapid, and the equilibration rates are seen to be quicker for compounds that have higher vapor pressures. The release of VOCs from the leaves of plants is slower for hyperbioconcentration leaves.     

Catalytic combustion of volatile organic compounds

Despite the success of adsorption and thermal incineration of (C)VOC emissions, there is still a need for research on techniques which are both economically more favorable and actually destroy the pollutants rather than merely remove them for recycling elsewhere in the biosphere. The catalytic destruction of (C)VOC to CO2, H2O and HCl/Cl2 appears very promising in this context and is the subject of the present paper. The experiments mainly investigate the catalytic combustion of eight target compounds, all of which are commonly encountered in (C)VOC emissions and/or act as precursors for the formation of PCDD/F. Available literature on the different catalysts active in the oxidation of (C)VOC is reviewed and the transition metal oxide complex V2O5-WO3/TiO2 appears most suitable for the current application. Different reactor geometries (e.g. fixed pellet beds, honeycombs, etc.) are also described. In this research a novel catalyst type is introduced, consisting of a V2O5-WO3/TiO2 coated metal fiber fleece. The conversion of (C)VOC by thermo-catalytic reactions is governed by both reaction kinetics and reaction equilibrium. Full conversion of all investigated VOC to CO2, Cl2, HCl and H2O is thermodynamically feasible within the range of experimental conditions used in this work (260-340 degrees C, feed concentrations 30-60 ppm). A first-order rate equation is proposed for the (C)VOC oxidation reactions. The apparent rate constant is a combination of reaction kinetics and mass transfer effects. The oxidation efficiencies were measured with various (C)VOC in the temperature range of 260-340 degrees C. Literature data for oxidation reactions in fixed beds and honeycomb reactors are included in the assessment. Mass transfer resistances are calculated and are generally negligible for fleece reactors and fixed pellet beds, but can be of importance for honeycomb monoliths. The experimental investigations demonstrate: (i) that the conversion of the hydrocarbons is independent of the oxygen concentration, corresponding to a zero-order dependency of the reaction rate; (ii) that the conversion of the hydrocarbons is a first-order reaction in the (C)VOC; (iii) that the oxidation of the (C)VOC proceeds to a higher extent with increasing temperature, with multiple chlorine substitution enhancing the reactivity; (iv) that the reaction rate constant follows an Arrhenius dependency. The reaction rate constant kr (s(-1)) and the activation energy E (kJ/mol) are determined from the experimental results. The activation energy is related to the characteristics of the (C)VOC under scrutiny and correlated in terms of the molecular weight. The kr-values are system-dependent and hence limited in design application to the specific VOC-catalyst combination being studied. To achieve system-independency, kr-values are transformed into an alternative kinetic constant K (m3/(m2u)) expressed per unit of catalyst surface and thus independent of the amount of catalyst present in the reactor. Largely different experimental data can be fitted in terms of this approach. Results are thereafter used to define the Arrhenius pre-exponential factor A*, itself expressed in terms of the activation entropy. Destruction efficiencies for any given reactor set-up can be predicted from E- and A*-correlations. The excellent comparison of predicted and measured destruction efficiencies for a group of chlorinated aromatics stresses the validity of the design approach. Since laboratory-scale experiments using PCDD/F are impossible, pilot and full-scale tests of PCDD/F oxidation undertaken in Flemish MSWIs and obtained from literature are reported. From the data it is clear that: (i) destruction efficiencies are normally excellent; (ii) the efficiencies increase with increasing operating temperature; (iii) the higher degree of chlorination does not markedly affect the destruction efficiency. Finally, all experimental findings are used in design recommendations for the catalytic oxidation of (C)VOC and PCDD/F. Predicted values of the a)VOC and PCDD/F. Predicted values of the acceptable space velocity correspond with the cited industrial values, thus stressing the validity of the design strategy and equations developed in the present paper.     

Synthesis of Co3O4 nanowire arrays supported on Ni foam for removal of volatile organic compounds

Crystalline Co3O4 nanowire arrays freely supported on Ni foam are successfully synthesized using a template-free method. The effects of reaction time, concentration of reactants, and temperature on the morphology of the nanowires are studied. The results indicate that uniform Co3O4 nanowires could be synthesized at 90 degrees C, and a transformation of the samples' morphology from nanoparticles to nanowires to microrods is observed by controlling the concentration of the reactants. The well-ordered nanowires synthesized under the selected reaction conditions are composed of spinel Co3O4 with diameters of 500-580 nm and lengths of 6-8 microm. These nanowires show good catalytic activity for the ozone catalytic oxidation of toluene.     

有机蒸气分离膜的应用

介绍了有机蒸气分离膜的分离原理，并分别介绍了有机蒸气分离膜在石油化工和聚氯乙烯行业中的应用．     

Micropatterned polymeric gratings as chemoresponsive volatile organic compound sensors: implications for analyte detection and identification via diffraction-based sensor arrays

Micropatterned polymeric diffraction gratings have been fabricated and evaluated as volatile organic chemical sensors. When operated under nonresonant conditions, sensor elements were found to respond in a rapid (response time 5-15 s) and reproducible fashion to each analyte investigated. Relative response magnitudes were found to be in qualitative agreement with those obtained via surface acoustic wave techniques. Preliminary limits of detection as determined by investigations with micropatterned polyepichlorohydrin, polyisobutylene, and polybutadiene gratings, respectively, were found to be 8, 11, and 7 ppm for toluene, 25, 258; and 72 ppm for methyl ethyl ketone; 41, 102, and 34 ppm for chloroform; and 460, 60, and 59 ppm for hexane. While generally less than 1 order of magnitude higher than those observed for identical polymer/analyte combinations in SAW studies, the observed limits of detection were at or below governmental standards (OSHA-PEL and NIOSH-REL) for each analyte evaluated. These diffraction-based sensors show promise for integration into an array-based sensor system, providing simultaneous identification and quantification of unknown analytes and simple analyte mixtures.     

Complementary metal oxide semiconductor cantilever arrays on a single chip: mass-sensitive detection of volatile organic compounds

The sensing behavior of polymer-coated resonant cantilevers for mass-sensitive detection of volatile organic compounds was investigated. Industrial complementary metal oxide semiconductor (CMOS) technology combined with subsequent CMOS-compatible micromachining was used to fabricate a single-chip system comprising the transducers and all necessary driving and signal-conditioning circuitry. An analytical model was developed to describe the mass-sensing mechanism of polymer-coated resonant cantilevers. The model was validated by measurements of various gaseous analytes. As an exemplary application, the quantitative analysis of a binary mixture using an array of four cantilevers is described. Experimental results are given for the concentration prediction of a mixture of n-octane and toluene. Finally, it was established that the limit of detection achieved with cantilever sensors is comparable to that of other acoustic wave-based gas sensors.     

室内空气中挥发性有机物测定的研究进展

本文对室内空气中挥发性有机物测定的研究进展包括室内空气中挥发性有机物的定义、来源、危害、限量标准、采样方法、分析方法、存在的问题及发展方向等作了较全面的介绍，重点介绍了国内外室内空气中挥发性有机物的分析测试技术，特别是光离子化检测器（PID）及其应用前景。     

Electrospun polyurethane fibers for absorption of volatile organic compounds from air

Electrospun polyurethane fibers for removal of volatile organic compounds (VOC) from air with rapid VOC absorption and desorption have been developed. Polyurethanes based on 4,4-methylenebis(phenylisocyanate) (MDI) and aliphatic isophorone diisocyanate as the hard segments and butanediol and tetramethylene glycol as the soft segments were electrospun from their solutions in N,N-dimethylformamide to form micrometer-sized fibers. Although activated carbon possessed a many-fold higher surface area than the polyurethane fiber meshes, the sorption capacity of the polyurethane fibers was found to be similar to that of activated carbon specifically designed for vapor adsorption. Furthermore, in contrast to VOC sorption on activated carbon, where complete regeneration of the adsorbent was not possible, the polyurethane fibers demonstrated a completely reversible absorption and desorption, with desorption obtained by a simple purging with nitrogen at room temperature. The fibers possessed a high affinity toward toluene and chloroform, but aliphatic hexane lacked the necessary strong attractive interactions with the polyurethane chains and therefore was less strongly absorbed. The selectivity of the polyurethane fibers toward different vapors, along with the ease of regeneration, makes them attractive materials for VOC filtration.     

Decomposition of volatile organic compounds in a plasma-catalytic reactor

A combined plasma-catalytic reactor was used for purification of air. The air was circulated through a grained catalyst, in which a pulsed-discharge plasma was excited at one time at atmospheric pressure. Acetone, ethyl lactate, and propylene glycol monomethylethyl acetate were used as impurities. The dry air and saturated humid air were purified. Results on the decomposition of the impurities with the use of a heated catalyst and a plasma in an inert filling material were also obtained. The combined reactor showed points in its favor for the purification conditions realized at a relatively small specific power consumption of ~100 J/liter. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 2, pp. 358–363, March–April, 2009.     

Photodecomposition of volatile organic compounds using TiO2 nanoparticles

This study examined the photodecomposition of volatile organic compounds (VOCs) using TiO2 catalyst fabricated by the Submerged Arc Nanoparticle Synthesis System (SANSS). TiO2 catalyst was employed to decompose volatile organic compounds and compare with Degussa-P25 TiO2 in terms of decomposition efficiency. In the electric discharge manufacturing process, a Ti bar, applied as the electrode, was melted and vaporized under high temperature. The vaporized Ti powders were then rapidly quenched under low-temperature and low-pressure conditions in deionized water, thus nucleating and forming nanocrystalline powders uniformly dispersed in the base solvent. The average diameter of the TiO2 nanoparticles was 20 nm. X-ray diffraction analysis confirmed that the nanoparticles in the deionized water were Anatase type TiO2. It was found that gaseous toluene exposed to UV irradiation produced intermediates that were even harder to decompose. After 60-min photocomposition, Degussa-P25 TiO2 reduced the concentration of gaseous toluene to 8.18% while the concentration after decomposition by SANSS TiO2 catalyst dropped to 0.35%. Under UV irradiation at 253.7 +/- 184.9 nm, TiO2 prepared by SANSS can produce strong chemical debonding energy, thus showing great efficiency, superior to that of Degussa-P25 TiO2, in decomposing gaseous toluene and its intermediates.     

Study on photocatalytic degradation of several volatile organic compounds

The gas-phase photolytic and photocatalytic reactions of several aromatics and chlorohydrocarbons were investigated. The experimental results revealed that chlorohydrocarbons like trichloroethylene, dichloromethane and chloroform could be degraded through either photolysis or photocatalysis under irradiation of germicidal lamp, and the elimination rate of chlorohydrocarbons through photolysis was quicker than that through photocatalysis. UV light from a germicidal lamp could directly lead to degradation of toluene but could hardly act on benzene. The photodegradation rate for these volatile organic compounds (VOCs) through photolysis followed an order: trichloroethylene>chloroform>dichloromethane>toluene>benzene>carbon tetrachloride, and through photocatalysis followed: trichloroethylene>chloroform>toluene>dichloromethane>benzene>carbon tetrachloride. Besides, a series of modified TiO2 photocatalysts were prepared by depositing noble metal, doping with transition metal ion, recombining with metal oxides and modifying with super strong acid. Activity of these catalysts was examined upon photocatalytic degradation of benzene as a typical compound that was hard to be degraded. It indicated that these modification methods could promote the activity of TiO2 catalyst to different extent. The apparent zero-order reaction rate constant for degrading benzene over SnO2/TiO2 catalyst had the highest value, which was nearly three times as that over P25 TiO2. But it simultaneously had the lowest rate for mineralizing the objective compound. In spite that Fe3+/TiO2 catalyst behaved slightly less active than SnO2/TiO2 for degradation of benzene, the mineralization rate over Fe3+/TiO2 was the highest one among the prepared catalysts.     

Development of a cryogen-free concentration system for measurements of volatile organic compounds

An innovative cryogen-free concentrator system for measurement of atmospheric trace gases at the parts per trillion level has been developed with detection by routinely used gas chromatographic methods. The first-generation system was capable of reaching a trapping temperature of -186 degrees C, while the current version can reach -195 degrees C. A Kleemenko cooler is used to create liquid nitrogen equivalent trapping conditions and eliminate the use of solid absorbents, a potential source of artifacts. The method utilizes dual-stage trapping with individual cold regions. The two stages are cooled to -20 and -175 degrees C for water management and sample enrichment, respectively. Both stages house a Silonite-coated stainless steel sample loop; the second stage loop is filled with 1-mm-diameter glass beads, which provide an inert surface area for analyte concentration. In our application, the complete system employed four channels utilizing two flame ionization detectors, one electron capture detector, and a mass spectrometer. The system was automated for unattended operation and was deployed off the New England east coast on Appledore Island to measure a suite of ambient non-methane hydrocarbons, halocarbons, alkyl nitrates, and oxygenated volatile organic compounds during the International Consortium for Atmospheric Research on Transport and Transformation field campaign in summer 2004. This robust system quantified 98 ambient volatile organic compounds with precisions ranging from 0.3 to 15%.     

Application of an array sensor based on plasma-deposited organic film coated quartz crystal resonators to monitoring indoor volatile compounds

The basic response ability of an array sensor based on plasma-deposited organic film-coated quartz crystal resonators (QCRs) was investigated with a view to their use for indoor air monitoring. The array of plasma-deposited organic film-coated QCRs was applied to detect and separate volatile organic compounds (VOCs) including alkanes, aromatic carbons, chlorocarbons, ketones, and alcohols. Continuous monitoring tests were tried in a real room environment (a refreshment area and a smoking area) with an array of plasma-deposited organic film-coated QCRs along with commercial sensors for indoor monitoring, a relative humidity/temperature sensor, a carbon dioxide sensor, and a three-dimensional micro-ultrasonic airflow meter. To provide a comparison commercial VOC detectors based on a photo-ionization detector and a semiconductor for indoor monitoring tests were used. The plasma-deposited organic film-coated QCRs exhibited fast pulse responses to volatile compounds in the room air along the baseline shift correlated with relative humidity changes and more sensitive responses compared with commercial organic gas detectors.     

A bibliometric analysis of world volatile organic compounds research trends

This study explores a bibliometric approach to quantitatively assessing current research trends on volatile organic compounds, by using the related literature in the Science Citation Index (SCI) database from 1992 to 2007. The articles acquired from such literature were concentrated on the general analysis by scientific output, the research performances by countries, institutes, and collaborations, and the research trends by the frequency of author keywords, words in title, words in abstract, and keywords plus. Over the past years, there had been a notable growth trend in publication outputs, along with more participation and collaboration of countries and institutes. Research collaborative papers had shifted from the national inter-institutional to the international collaboration. Benzene, toluene, and formaldehyde were the three kinds of VOCs concerned mostly. Detection and removing, especially by adsorption and oxidation, of VOCs were to be the orientation of all VOCs research in the next few years.